"Bottom-Up" Design of Nanostructured Conducting Polymer Thin Films

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TECHNICAL SUMMARY:Effective control of nanoscale morphology of organic semiconducting polymer thin films is an important prerequisite for designing more efficient thin-film devices including organic light-emitting and photovoltaic devices. The current "top-down" paradigm to such devices is based on utilizing solution-based processing of soluble semiconducting polymers. This approach generally provides only modest control over nanoscale molecular organization and phase separations. A potentially transformative alternative to using solutions of pre-synthesized conjugated polymers would be a "bottom-up" approach to prepare surface-grafted thin films of conjugated polymers by surface-initiated polymerization of small-molecule monomers. The ultimate goal of this project is to develop a modular, bottom-up strategy to surface-immobilized nanostructured semiconducting polymer thin-film materials with hierarchically controlled molecular organization. This strategy includes a combination of nanosphere lithographic patterning with surface-initiated in situ polymerization through simple and efficient chemistries. The project focuses on the following specific aims: (1) studies on nanosphere lithography as a method to prepare nanopatterned immobilized monolayers of semiconducting polymer precursors; (2) development of methods to convert the precursor monolayers into surface-immobilized nanostructured films of semiconducting polymers by using chemical (such as metal-catalyzed living polymerization and/or "click" chemistry) or electrochemical approaches; (3) applying the outcomes of (1) and (2) to design a bottom-up modular strategy to preparation of bulk heterojunction thin-film solar cells. Realization of these goals is being done through broad-range fundamental studies on mechanisms and conditions of the surface-initiated polymerization aimed at improving both the molecular parameters of the conjugated polymers and bulk molecular organization in the thin films. The outcome of these studies may create a new paradigm for design of polymer thin-film materials for organic electronics through the efficient and precise control over molecular structure and nanoscale organization in the polymer films.NON-TECHNICAL SUMMARY:Despite the recent advances in the field of organic semiconducting polymers, it is still far from offering a real economically viable alternative to inorganic materials. This interdisciplinary project will directly impact the national energy security by developing new potentially promising approaches to preparing thin-film organic polymer materials for photovoltaic applications. This can potentially lead to efficient and reliable organic polymer solar cells. While this should be seen as a major practical outcome of this project, it is also aimed to contribute to development and fundamental understanding of surface-initiated polymerization, as well as processes of nanoscale organization in complex organic materials. The students will be trained in organic synthesis, device fabrication techniques, materials and device characterization, and will learn modern theoretical and computational methods. They will acquire and develop strong multidisciplinary skills and expertise required to be competitive in the current high-tech job market. Beyond that, students working on this project will be involved in a variety of ongoing broader activities with the goal to improve public awareness and appreciation of modern science and technology and its impact on people's lives, and create interest in science, especially to younger generations. This will be done through various community outreach programs such as lectures and demonstrations in public schools, with a particular emphasis on underperforming schools.